Notches (often used to stimulate crack-like defects) in pipes are characterized using Helical-Guided Ultrasonic Waves (HGUW). In thin-walled curved structures with a radius-to-thickness ratio of more than 10/1, Lamb-type guided waves, called the HGUW, propagate. HGUW are plane-strain guided waves propagating circumferentially in helical paths in large-diameter cylindrical structures, with the properties of Lamb waves. They travel in multiple trajectories between two points, and these paths are indexed as orders of the helical path. When the HGUW encounters a notch in its path, it scatters, and the information in the scattering is used to characterize the notch (i.e., determine the notch size). In this work, an approach called the stepped wavelength method is presented to determine the notch size. In this approach, the directivity plots, quantifying from the scattering of the HGUW in all directions around the notch, are evaluated for a set of frequencies (each corresponding to a specific wavelength) from the numerical model of the pristine and damaged pipes. As the wavelength-to-notch size ratio approaches one and increases beyond that, a change in the directivity plot’s profile is witnessed, suggesting a change in the nature of the interaction between the notch and the incident wave. A criterion based on the change in the nature of interaction is developed to estimate the notch size.
This work presents acoustic emission (AE) waveform to source coordinates transformation at hollow cylinders facilitated by multiple Lamb mode arrivals due to the cylindrical geometry. Variational autoencoder (VAE) is selected to perform waveform source discrimination by capturing the delays in time-of-flights (TOF) between modes described in the transformation. An AE waveform dataset simulated by pencil lead break on a liquid nitrogen tank was collected to validate the proposed approach. The result indicates that VAE is capable of separate AE waveforms by their sources through the targeted delays between mode arrivals.
This paper presents solutions for guided wave motion (Lamb and shear horizontal) due to tensile and shear cracks in an isotropic plate using elastodynamic reciprocity. Finite-length through-thickness cracks are considered via Huygens’ principle by representing them as a superposition of point cracks. Far-field solutions are then derived in order to simplify the results and facilitate a direct comparison of guided mode excitability due to various cracking modes. Relatively short- and long-length line cracking are compared to point cracking for the fundamental modes S0, A0, and SH0. It is shown that the A0 modal response is the most sensitive to crack length, with S0 and SH0 being relatively insensitive. Additionally, the radiation patterns of S0, A0, and SH0 are relatively insensitive to crack length. The results have applications in acoustic emission monitoring of plate-like structures, where modal responses may be used to characterize crack growth.
Condition assessment of pipeline networks is critical to ensure operation safety considering that the network around the US is aging. This work aims at combining guided ultrasonic waves and advanced tomographic algorithms to locate corrosion-induced defects in both inner and outer surfaces of steel pipes. Particularly, it employs guided ultrasonic waves that propagate on helical paths around pipes. The novelty of this work is in using high orders of the so-called helical guided ultrasonic waves (HGUW), which can significantly increase the inspection area with a minimum number of sensors. Algebraic reconstruction technique (ART) is then implemented in order to gather information from the wave propagation through the pipe and asses possible locations where defects might exist. To validate the proposed imaging algorithm, numerical simulation and experiments were carried out. The final results suggest that the proposed imaging algorithm can be effectively used for continuous monitoring of corrosion damage in pipelines.
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